Power-window jamming preventing apparatus

ABSTRACT

A power-window jamming preventing apparatus, includes a current sensing circuit, which senses a motor current flowing through a motor; a current limiting circuit, which increases and decreases the motor current based on a current-limitation control signal outputted from the current sensing circuit when an amount of increase of the motor current exceeds a predetermined vale; and a jamming determining circuit, which determines a jamming of a foreign matter in the window glass, and a potential difference generating circuit, which monitors a power source voltage supplied to the current sensing circuit and the power window motor, and which clamps a third reference voltage so as to drop a constant voltage from the third reference when the power source is low such that a potential difference between the second reference voltage and the third reference voltage is kept greater than a predetermined voltage.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for preventing a jammingof a foreign matter (e.g., finger, neck, or the like of the passenger)in a power window of a vehicle and, more particularly, improvement in apower-window jamming preventing apparatus for determining quickly ajamming of a foreign matter without error.

An apparatus for automatically opening/closing a window glass of avehicle is normally called a power window, and is an apparatus thatopens/closes the window glass by a motor. A power-window jammingpreventing apparatus is employed to provide the jamming protection tothe power window as the countermeasure to prevent the jamming of theforeign matter in the window glass. In the normal power-window jammingpreventing apparatus, the load applied to the jammed foreign matter isextremely increased because of an increase of the motor current when thejamming of the foreign matter occurs during the lifting of the windowglass, and therefore the motor current must be limited to suppress suchincrease of this motor current.

Therefore, the power-window jamming preventing apparatuss improved totake account of the above circumstances were proposed (for example, seeJP-A-2002-295129).

In the description in the following drawings, the same or like symbolsare affixed to the same or functionally like portions.

The power-window jamming preventing apparatus proposed inJP-A-2002-295129 will be explained in detail with reference to theaccompanying drawings hereunder.

(Outline of the Power-window Jamming Preventing Apparatus)

FIG. 3 is a block diagram of an example of the power-window jammingpreventing apparatus proposed in JP-A-2002-295129. This power-windowjamming preventing apparatus has an abnormal current (generated by ajamming, or the like) sensing circuit 2, a power-window motor 5 having aforwarding/reversing circuit, a jamming determining circuit 6, and amotor current limiting circuit 7. In this case, the power-window motor 5having the forwarding/reversing circuit may be considered as theforwarding/reversing circuit 5 containing the power-window motor. Threecircuits of the current sensing circuit 2, the forwarding/reversingcircuit 5, and the current limiting circuit 7 are connected in serieswith an electric wire 1 through which a motor current ID flows, and areconnected to a power supply device VB.

(Outline of the Abnormal Current (Generated by the Jamming, or the Like)Sensing Circuit 2)

The current sensing circuit 2 senses an abnormal current generated inthe motor current ID by the jamming, or the like, and then outputs anabnormal current sensing signal (current-limitation control signal) tothe current limiting circuit 7 via a signal line 9. The current sensingcircuit 2 has a multi-source field effect transistor (FET) or a multiresistor, a current following circuit 3, and a starting circuit 4.

The multi-source FET is composed of a main FET and a reference FET.Also, the multi resistor is composed of a shunt resistor and a referenceresistor. A current sensing ratio n of the multi-source FET or the multiresistor, i.e., a resistance component ratio of the reference resistorto the main resistor, for example, is set in excess of 1, preferably setto 100 or more. The motor current ID is supplied to the main FET or theshunt resistor. Then, a reference current Iref is controlled in such amanner that the reference current Iref that satisfies a condition ofID=n*Iref flows through the reference FET or the reference resistor.

In the case where the main FET or the shunt resistor is present on thehigh side of the motor (the power supply side with respect to themotor), a source potential of the main FET or a motor-side potential VSAof the shunt resistor and a source potential of the reference FET or aground-side potential VSB of the reference resistor must be set tosatisfy a condition of VSA=VSB so as to satisfy the above conditionID=n*Iref. If the motor current ID is changed owing to change in adriving force of the window glass when the motor is normally running,the source potential VSA of the main FET, etc. are also changed, but thecondition of VSA=VSB is maintained by controlling the reference currentIref.

Next, a method of sensing the abnormal current generated by the jamming,or the like will be explained hereunder. The reference current Iref isclassified into two current components each having a different followingspeed. The reference current Iref is classified into a current componentIref-s having a slow following speed and a current component Iref-fhaving a fast following speed. The current component Iref-s having aslow following speed is set such that such component follows the changein the motor current ID when the motor is normally running but cannotfollow sudden change of the motor current ID when the jamming occurs. Incontrast, the current component Iref-f having a fast following speed isset such that such component can follow not only change in the currentwhen the jamming occurs but also a ripple component contained in themotor current ID. If the following characteristic of the currentcomponent Iref-f having a fast following speed is improved more andmore, the current component Iref-s having a slow following speed is notneeded to change and is stabilized. In order to satisfy such condition,the following speed of the current component Iref-f having a fastfollowing speed is set 800 to 1000 times quicker than the currentcomponent Iref-s having a slow following speed.

When setting in this manner, the current component Iref-f having a fastfollowing speed reflects exactly the change in the motor current IDexcept the ON/OFF operation of the semiconductor switching element. Thechange in the motor current ID is converted into a voltage by passingthe current component Iref-f having a fast following speed through aresistor having a resistance value larger than the reference resistor.An amplified variation of an infinitesimal variation obtained byconverting the change in the motor current ID into a voltage via an ONresistance of the shunt resistor or the main FET can be sensed by theconversion of this voltage.

When the jamming occurs, the current component Iref-f having a fastfollowing speed is increased to follow the motor current ID, while thecurrent component Iref-s having a slow following speed is seldomchanged. As a result, a difference is generated between an average valueof the current component Iref-f having a fast following speed and thecurrent component Iref-s having a slow following speed, and thus amagnitude relationship of (average value of Iref-f)>(Iref-s) is derived.If this magnitude difference exceeds a previously set value, theabnormal current sensing signal is generated and then the multi-sourceFET placed on the high side of the motor or the semiconductor switchingelement (the FET or the bipolar transistor) in the current limitingcircuit 7 placed on the low side of the motor is turned off.

Then, the multi-source FET or the semiconductor switching element placedon the low side of the motor execute the operation to repeat the ON/OFFoperation and the continuous ON operation during when the jammingoccurs. Although explained in detail hereunder, the increase of themotor current ID can be limited by the operation to repeat the ON/OFFoperation and the continuous ON operation.

(Outline of the Motor Current Limiting Circuit 7)

The current limiting circuit 7, when receives the abnormal currentsensing signal, limits the current not to increase the motor current ID.This limitation is executed by causing the multi-source FET or thesemiconductor switching element placed on the low side of the motor torepeat alternately the ON/OFF operation and the continuous ON operation.The operation signal to repeat the ON/OFF operation and the continuousON operation is output to the jamming determining circuit 6 via a signalline 10. The current limiting circuit 7 has the semiconductor switchingelement such as FET, or the like for ON/OFF-controlling the motorcurrent ID, and a reference voltage circuit 8 for generating an ONreference voltage and an OFF reference voltage of the semiconductorswitching element.

When the motor current ID enters into the repeating operation of theON/OFF operation and the continuous ON operation, such motor current IDis limited to keep an average value at a value that is slightly largerthan a value obtained immediately before the jamming occurs. A motortorque is in proportion to the motor current, and accordingly the motortorque is kept at a torque that is slightly larger than a torquerequired for the drive of the window glass. If such required minimumtorque is ensured, the minimum jamming load can be realized under thecondition that the false reversion is not caused even though a glassdriving force is momentarily varied due to the rough road, or the like.

(Outline of the Jamming Determining Circuit 6)

The jamming determining circuit 6 determines whether or not the jammingoccurred, based on the input operation signal to repeat the ON/OFFoperation and the continuous ON operation. The jamming determiningcircuit 6, when determines that the jamming occurred, outputs awindow-down signal to the effect that the window glass is opened to theforwarding/reversing circuit 5 via a signal line 11.

In the determination of the jamming, such an event is utilized that aperiod of the ON/OFF operation of the semiconductor switching element isprolonged and a period of the continuous ON operation of thesemiconductor switching element is shortened while the number ofrevolution of the motor is lowered owing to the jamming. For example,when the period of the ON/OFF operation comes up to a predeterminedlength, it is decided that the jamming occurred. When the occurrence ofthe jamming is determined, the motor 5 is stopped by shutting off themulti-source FET or the semiconductor switching element, and then themotor 5 is reversed/driven after a predetermined time lapsed.Accordingly, the window glass is opened and the inserted foreign mattercan be prevented from being jammed.

(Outline of the Power-window Motor 5 Having the Forwarding/reversingCircuit)

The forwarding/reversing circuit 5 runs the motor in the direction toclose the window glass by inputting a window-up signal, and runs themotor in the direction to open the window glass by inputting awindow-down signal. Also, the forwarding/reversing circuit 5, whenreceives the window-down signal via the signal line 11, inverts therevolution of the motor from the direction to close the window glass tothe direction to open the window glass. The forwarding/reversing circuit5 has an H-bridge circuit or a relay circuit. When the H-bridge circuitis used, four FETs to constitute or connect the H-bridge circuit areused. The current sensing circuit 2 and the current limiting circuit 7may be constructed by using the transistor on the high side out of fourFETs, or the current sensing circuit 2 may be constructed by using thetransistor on the high side and the current limiting circuit 7 may beconstructed by using the transistor on the low side.

FIGS. 4A to 4C show a variation of a block diagram of the power-windowjamming preventing apparatus. More particularly, the current sensingcircuit 2 is connected to a plus terminal of the power supply device VBor a ground that is equivalent to a minus terminal, and the sequence inwhich the motor current ID is supplied to the forwarding/reversingcircuit 5 and the current limiting circuit 7 may be set arbitrarily.More particularly, the sequence like the current sensing circuit 2→thecurrent limiting circuit 7→the forwarding/reversing circuit 5, as shownin FIG. 4A, the sequence like the current sensing circuit 2→theforwarding/reversing circuit 5→the current limiting circuit 7 (i.e., thesame sequence as shown in FIG. 3), as shown in FIG. 4B, the sequencelike the forwarding/reversing circuit 5→the current limiting circuit7→the current sensing circuit 2, as shown in FIG. 4C, and others may beselected. It may be concluded that no large difference of the action andthe effect of the power-window jamming preventing apparatus is causedbecause of the difference of the sequence.

FIG. 5 shows an example of a circuit diagram of the power-window jammingpreventing apparatus. The circuit configurations and the circuitoperations of the current sensing circuit 2, the current limitingcircuit 7, and the jamming determining circuit 6 in the power-windowjamming preventing apparatus will be explained in detail herein.

1. Explanation of the Current Sensing Circuit 2

1-1. Circuit Configuration of the Current Sensing Circuit 2

A circuit for classifying the reference current Iref into two currentcomponents Iref-s and Iref-f each having the different following speedby using the shunt resistor and the reference resistor to sense theabnormal current will be explained hereunder.

The current sensing circuit 2 in FIG. 5 has a shunt resistor R1 and areference resistor R20 both connected to the plus terminal of the powersupply device VB, a current following circuit 3 connected to theresistors R1 and R20, a comparator CMP2 whose plus input terminal andminus input terminal are connected to the current following circuit 3and whose output terminal is connected to the current limiting circuit7, and a resistor R25 connected between a 5V power supply and the outputterminal of CMP2.

The current following circuit 3 has a comparator CMP1 whose plus inputterminal is connected to the reference resistor R20 and whose minusinput terminal is connected to the shunt resistor R1, a firstcharging/discharging circuit constructed by connecting a resistor R21and a grounded capacitor C1 in series and connected to an outputterminal of CMP1, a second charging/discharging circuit constructed byconnecting a resistor R22 and a grounded capacitor C2 in series andconnected to the output terminal of CMP1, a resistor R28 connectedbetween the capacitors C1 and C2, an nMOSFET (T21) whose drain terminalis connected to the plus input terminal of CMP1 and whose gate terminalis connected to the capacitor C1, a first source follower circuitconstructed by a resistor R23 whose one end is connected to a sourceterminal of FET (T21) and the plus input terminal of CMP 2 and whose theother end is grounded, an nMOSFET (T22) whose drain terminal isconnected to the plus input terminal of CMP1 and whose gate terminal isconnected to the capacitor C1, a diode D21 whose anode terminal isconnected to a source terminal of FET (T22), and a second sourcefollower circuit constructed by a resistor R24 whose one end isconnected to a cathode terminal of the diode D21 and the minus inputterminal of CMP 2 and whose the other end is grounded.

In this case, 910K labeled to the resistor R21, etc. in FIG. 5 denotesthat a resistance value of the resistor R21 is 910 KΩ. Similarly, 0.1 uflabeled to the capacitor C2, etc. denotes that a capacitance value ofthe capacitor C2 is 0.1 μF.

1-2. Explanation of an Operation of the Current Sensing Circuit 2

In FIG. 5, the shunt resistor R1, the forwarding/reversing circuit 5,and a semiconductor switching element (FET) T1 used to execute theON/OFF operation are connected in series with the electric wire 1,through which the motor current ID flows, and connected between the plusterminal and the minus terminal of the power supply device (e.g.,battery) VB. Forwarding/reversing relays in the forwarding/reversingcircuit 5 are driven by transistors T2 and T3 respectively, and T2 isturned ON in the forwarding (up) operation while T3 is turned ON in thereversing (down) operation. The multi resistor is composed of the shuntresistor R1 and the reference resistor R20. In the circuit example inFIG. 5, a resistance value of R1 is set to 34 mΩ, and a resistance valueof R20 is set to 55Ω. The motor current ID flows through the shuntresistor R1 and the reference current Iref flows through the referenceresistor R20. For convenience of explanation, the resistance value ofthe resistor R1, the capacitance value of the capacitor C2, and othersare represented by the same symbol R1 as the resistor R1, and others.Thus, the current ratio n to satisfy the condition of R1*ID=R20*Iref isgiven by Eq.(1).n=ID/Iref=R 20/R 1=55/0.034=1618   Eq.(1)

The comparator CMP1 consists of an OP amplifier, and a motor-sidepotential of the shunt resistor R1 is input into the minus inputterminal of CMP1 and a ground-side potential of the reference resistorR20 is input into the plus input terminal of CMP1. The firstcharging/discharging circuit constructed by connecting the resistor R21and the capacitor C1 in series is connected to between the output ofCMP1 and a ground potential level (GND), and the capacitor C1 ischarged/discharged by an output (charge/discharge control signalCMP1_OUT) of CMP1 via the resistor R21. The non-grounded side of thecapacitor C1 is connected to the gate terminal of FET T21, the drainterminal of FET T21 is connected to the reference resistor R20, and thesource terminal of FET T21 is grounded via the resistor R23. Since FETT21 and the resistor R20 constitute the first source follower circuit, acurrent that is proportional to a potential of the capacitor C1 flowsthrough FET T21 and the resistor R20. This current serves as the currentcomponent Iref-s having a slow following speed in the reference currentIref. In contrast, the second charging/discharging circuit constructedby connecting the resistor R22 and the capacitor C2 in series isconnected to between the output of CMP1 and the ground potential level(GND), and the capacitor C2 is charged/discharged by the output of CMP1via the resistor R22. The non-grounded side of the capacitor C2 isconnected to the gate terminal of FET T22, the drain terminal of FET T22is connected to the reference resistor R20, and the source terminal ofFET T22 is grounded via the resistor R24. Since FET T22, the diode D21,and the resistor R24 constitute the second source follower circuit, acurrent that is proportional to a potential of the capacitor C2 flowsthrough FET T22, the diode D21, and the resistor R24. This currentserves as the current component Iref-f having a fast following speed inthe reference current Iref. The non-grounded sides of the capacitors C1and C2 are connected via the resistor R28, so that potentials of thecapacitors C1 and C2 are made equal to each other when the motor currentID is not changed. In other words, two charging/discharging circuitsconsisting of the capacitors C1, C2 and the resistors R21, R22 areconnected in parallel to the output of the comparator CMP1, and twosource follower circuits that flow the current in proportion to thepotentials of respective capacitors C1 and C2 are connected in parallelbetween the reference resistor R20 and the ground. A time constant ofthe first charging/discharging circuit is set larger than that of thesecond charging/discharging circuit. In this circuit example, the timeconstant of the first charging/discharging circuit is given by Eq.(2)and the time constant of the second charging/discharging circuit isgiven by Eq.(3), and thus a ratio of time constants becomes 1:894.$\begin{matrix}\begin{matrix}{\begin{matrix}\left( {{Time}\quad{constant}\quad{of}\quad{the}} \right. \\{{first}\quad{{charging}/}} \\\left. {{discharging}\quad{circuit}} \right)\end{matrix} = \begin{matrix}{{R21}*{\left( {{R22} + {R28}} \right)/}} \\{\left( {{R21} + {R22} + {R28}} \right)*{C1}}\end{matrix}} \\{= {910\quad K*{\left( {{5.1\quad K} + {910\quad K}} \right)/}}} \\{\left( {{910\quad K} + {5.1\quad K} + {910\quad K}} \right)*} \\{1\quad{µf}} \\{= {456\quad{ms}}}\end{matrix} & {{Eq}.\quad(2)} \\\begin{matrix}{\begin{matrix}\left( {{Time}\quad{constant}\quad{of}\quad{the}} \right. \\{{second}\quad{{charging}/}} \\\left. {{discharging}\quad{circuit}} \right)\end{matrix} = {{R22}*{C2}}} \\{= {5.1\quad K*0.1\quad{µf}}} \\{= {0.51\quad{ms}}}\end{matrix} & {{Eq}.\quad(3)}\end{matrix}$

The jamming is sensed by the comparator CMP2. A source potential of T21is input into the plus input terminal of CMP2 and a potential that islower than the source potential of T22 by a forward voltage drop ofabout 0.7 V in the diode D21 is input into the minus input terminal.Because gate-source potentials of T21 and T22 are almost equal to eachother, an amount of the voltage drop in D21 corresponds to a sensedvalue of the abnormal current that is increased due to the jamming. Thecurrent component Iref-f is increased because of the occurrence of thejamming, an output (current-limitation control signal CPOUT_B) of CMP2is changed from an H level to an L level. Then, an output of a NOR1 inthe current limiting circuit 7 is shifted to an H level, a transistorT31 is turned ON, and the transistor T1 as the semiconductor switchingelement is turned OFF. The abnormal current generated due to the jammingat this time is sensed as follows.

(a) First, the reference current Iref is separated into the currentcomponent Iref-s having a slow following speed the current componentIref-f having a fast following speed, as shown in FIG. 5. The change ofthe motor current ID appears in the Iref-f to contain the ripplecomponent, and is reflected exactly in a source potential of T22, i.e.,a voltage (Vins) at the minus input terminal of CMP2. As a result, asource potential of T21 on the Iref-s side, i.e., a voltage (Vc) at theplus input terminal of CMP2 is not subjected to the influence of a fastvariation of the motor current ID, and reflects only an average valuetaken over a long period. Therefore, the above potential is kept at analmost constant potential while the current limitation is being carriedout after the jamming occurred, whereby the ideal reference voltage canbe realized.

(b) A variation component caused by the ripple component of the motorcurrent is contained in the current component Iref-f having a fastfollowing speed. Assume that an amplitude of the ripple current isΔID-rip and the ripple component of the Iref-f is ΔIref-f-rip,ΔIref-f-rip=ΔID-rip/n is satisfied. In the case where R24=1.5KΩ andΔID-rip=0.5 A, a voltage variation ΔVrip generated in the resistor R24by ΔIref-f-rip becomes 0.46 V, as given by Eq. (4). $\begin{matrix}\begin{matrix}{{\Delta\quad{Vrip}} = {\Delta\text{Iref-f-rip}*{R24}}} \\{= {\Delta{\text{ID-rip}/n}*{R24}}} \\{= {0.5\quad{A/1618}*1.5\quad K}} \\{= {0.46\quad V}}\end{matrix} & {{Eq}.\quad(4)}\end{matrix}$

That is, the voltage at the minus input terminal of CMP2 is oscillatedby the ripple component at an amplitude ±0.23V (±ΔVrip/2). Therefore,the output of CMP2 is inverted from the H level to the L level when theaverage value of the Iref-f is increased by 0.47V (=0.7V−0.23V).

This 0.47V is calculated as 0.51 A (=0.47V/R24*n=0.47V/1.5K*1618) interms of the motor current ID. That is, in the circuit example in FIG.5, when the average value of the motor ID is increased by 0.51 A due tothe jamming, the output of CMP2 is shifted to the L level and then T31is turned ON and T1 goes to its OFF state.

(c) As shown in FIGS. 6A to 6C, since the motor current is increasedbefore the output of CMP2 is inverted into the L level (prior to a timet1), the output of CMP2 is at the H level. When T31 is turned ON, themotor current ID start to decrease with delay corresponding to a timeduring when the charges that are excessively charged in the gate of T1are discharged. The output of CMP1 starts to shift from the H level tothe L level at this point of time. However, since CMP1 is composed ofthe OP amplifier, a delay time is generated owing to the delayedresponse of the OP amplifier when such output is changed from the Hlevel to the L level.

Since C2 is charged during a time t1 required until the output of CMP1is lowered from the H level and becomes equal to the potential of thecapacitor C2 after the output of CMP2 is inverted to the L level, theIref-f is increased and the voltage at the minus input terminal of CMP2is increased. Then, C2 starts to discharge when the output of CMP1becomes lower than the potential of C2. The voltage at the minus inputterminal of CMP2 goes back to the original voltage, i.e., the voltage atwhich the output of CMP2 is started to shift from the H level to the Llevel, after a time t2 required until the discharging of the chargesstored for the time t1 is completed. The voltage at the plus inputterminal is not changed during this time.

After the time t2 lapsed, the output of CMP2 is inverted to the H leveland also FET T1 is turned ON. That is, the output of CMP2 is kept at theL level for a time t1+t2 after the motor current ID is increased andthen the output of CMP2 is inverted to the L level. If the potential ofC2 is located between the H level and the L level of the output of CMP1,a relationship of t1≈t2 is derived. The time t1+t2 is decided dependentupon a turn-OFF delay time of T1, a response speed of the OP amplifier,and a decreasing rate of the motor current ID. In this case, because theturn-OFF delay time of T1 and the response speed of the OP amplifier areconstant, such time t1+t2 depends on the decreasing rate of the motorcurrent ID and becomes longer as the decreasing rate becomes slower.

When the output of CMP2 is shifter again from the L level to the H leveland also T1 is turned ON, the motor current ID starts to increase.Therefore, the output of CMP1 goes from the L level to the H level, butC2 is continued to discharge during when the output of CMP1 is lowerthan the potential of C2. Suppose that a time required until the outputof CMP1 becomes equal to the potential of the capacitor C2 after theoutput of CMP2 is inverted to the H level is a time t3. When the outputof CMP1 exceeds the potential of the capacitor C2, such capacitor C2 isstarted to charge. When a time t4 required until the charge having thesame charge quantity as that being discharged for the time t3 is chargedlapsed, the output of CMP2 is inverted to the L level and the T1 isturned OFF. In other words, the output of CMP2 is maintained at the Hlevel for the time t3+t4. The time t3+t4 is decided based on theresponse speed of the OP amplifier and an increasing rate of the motorcurrent ID. Because the response speed of the OP amplifier is constant,the time t3+t4 depends on the increasing rate of the motor current IDand is shortened smaller as the increasing rate is accelerated.

(d) The reason why the forward voltage drop of the diode D21 is used toset a jamming sensing value is to keep the jamming sensing valueconstant even though the motor current ID is changed and thus theaverage value of the Iref-f is changed. However, since the forwardvoltage drop of the diode D21 cannot be changed by this method when thejamming sensing value must be changed, such jamming sensing value ischanged by adjusting a resistance value of the resistor R24. Asunderstood from the explanation in the item (b), the jamming sensingvalue becomes small if the value of the resistor R24 is increasedwhereas the jamming sensing value becomes large if the value of theresistor R24 is decreased conversely.

(e) It is feasible to set the jamming sensing value by using a resistorin place of the diode D21. In this case, when the motor current ID isincreased, the jamming sensing value is increased in proportion to this.

2. Explanation of the Current Limiting Circuit 7

2-1. Circuit Configuration of the Current Limiting Circuit 7

The current limiting circuit 7 in FIG. 5 includes a NOR gate NOR1 whoseinput terminal is connected to the output terminal of CMP2, a comparatorCMP3 whose output terminal is connected to the input terminal of NOR1,the reference voltage circuit 8 connected to a minus input terminal ofCMP3, the semiconductor switching element T1 whose drain terminal isconnected to a plus input terminal of CMP3 and whose source terminal isgrounded, a variable resistor R32 connected to a gate terminal of theswitching element T1, an FET (T31) whose gate terminal is connected toan output terminal of NOR1, whose drain terminal is connected to theresistor R32, and whose source terminal is grounded, a resistor R31connected between the plus terminal of the power supply device VB andthe drain terminal, a resistor R33 connected between the plus inputterminal of CMP3 and the ground, and a resistor R37 connected betweenthe output terminal of CMP3 and the 5V power supply.

The reference voltage circuit 8 has a resistor R35 connected between theminus input terminal of CMP3 and the power supply device VB, a resistorR36 connected between the minus input terminal of CMP3 and the ground, aresistor R34 connected to the minus input terminal of CMP3, a diode D31whose anode terminal is connected to the resistor R34, and an FET (T32)whose drain terminal is connected to a cathode terminal of the diodeD31, whose source terminal is grounded, and whose gate terminal isconnected to the output terminal of CMP3.

2-2. Explanation of an Operation of the Current Limiting Circuit 7

The limitation of the motor current ID is carried out by using thecurrent sensing circuit 2 and the current limiting circuit 7 incombination.

At first, the operation of the current limiting circuit 7 will beexplained hereunder. When an output of the comparator CMP2 in thecurrent sensing circuit 2 is at the H level, an output of the NOR gateNOR1 becomes the L level, the transistor T31 is turned OFF, and theswitching element (transistor) T1 is turned ON. Explanation will be madeof the case where T1 is formed of FET. At this time, since the voltageat the plus input terminal of the comparator CMP3 is connected to thedrain terminal of T1, the almost ground potential level is input to theterminal. In contrast, the voltage at the minus input terminal of thecomparator CMP3 is decided by the reference voltage circuit 8 thatconsists of R34, R35, R36, the diode D31, and the transistor T32. WhenR34=3.3KΩ, R35=10KΩ, R36=24KΩ are set and the power supply voltage VB isset to 12.5V, such voltage becomes 8.82V if T32 is turned OFF while suchvoltage becomes 3.03V if T32 is turned ON. Since the voltage is neverlowered smaller than 3.03V in any case, the output of CMP3 is at the Llevel. Thus, T32 is in its OFF state. When the jamming occurs and theoutput of the comparator CMP2 goes to the L level, the output of NOR1goes to the H level, the T31 is turned ON, and the T1 is turned OFF. Thedrain voltage VDS of the. T1 starts to increase from the groundpotential level. Since T32 was turned OFF, the voltage at the minusinput terminal of the CMP3 is 8.82V. When the drain voltage VDS of T1goes to 8.82V or more, the output of CMP3 is inverted into the H level,the output of NOR1 goes to the L level, and T31 is turned OFF and T1 isturned ON. At this time, since T32 is also turned ON at the same time,the minus input voltage of CMP3 is lowered to 3.03V. As a result, T1holds its ON state until the drain voltage VDS is lowered to 3.03V orless once T1 is turned ON. When the drain voltage VDS of T1 is reducedlower than 3.03V, the output of CMP3 goes to the L level once again, T1is turned OFF and simultaneously T32 is turned OFF, and the minus inputterminal of CMP3 is increased up to 8.82V. T1 maintains its OFF stateuntil the drain voltage VDS of T1 exceeds 8.82V. This operationcorresponds to one period of the ON/OFF operation, and this state iscontinued inasmuch as the output of CMP2 is at the L level.

Constancy of the Motor Current in the ON/OFF Operation

Next, the event that the motor current ID is scarcely changed in oneperiod of the ON/OFF operation when the ON/OFF operation is executedwill be explained hereunder. A static characteristic curve to which aload line of FET T1 is added is shown in FIG. 7. When the motor isnormally running before the jamming occurs, T1 operates at an A point.When the motor load current ID is changed, the operating point movesvertically between the A point and a B point, for example, in the ohmicrange. When the jamming occurs, the load current ID of the motor isincreased and the operating point of T1 moves upward. When the operatingpoint comes up to the B point, T1 is turned OFF. A current differencebetween the B point and the A point shows the jamming sensing value.When T1 is turned OFF, the drain-source voltage VDS is extended but theoperating point of T1 at that time moves rightward on a horizontal linepassing through the B point. In other words, the drain current ID (=themotor load current) keeps as it is the value obtained when T1 is turnedOFF and the drain-source voltage VDS of T1 is extended. This is because,when the drain-source voltage VDS of T1 moves between the groundpotential level and the power supply voltage, the gate-drain capacitanceCGD of T1 is apparently increased by the Miller effect and thus thedrain-source voltage VDS is seldom changed.

Miller Effect

FIG. 8 is an equivalent circuit diagram of the switching element T1.Suppose that the drain-source voltage VDS is increased by aninfinitesimal voltage ΔVGS based on the charging executed via the gatedriver. Accordingly, the motor current ID is increased by ΔID and thus acounter electromotive force Ec (=L*dID/dt) is generated by an inductanceL of the motor. A charge ΔQ charged in the gate-drain capacitance CGD isgiven by Eq. (5).ΔQ=CGD*(ΔVGS+ΔID*Ra+Ec)  Eq.(5)where Ra is an armature resistance. Also, a capacitance Cm of CGD, whichis from the gate terminal, is given by Eq.(6).Cm=ΔQ/ΔVGS=CGD*(1+ΔID*Ra/ΔVGS+Ec/ΔVGS)  Eq.(6)

The capacitance Cm is the “Miller capacitance” and is the apparentcapacitance generated by the fact that a voltage change across thecapacitance CGD is considerably larger than ΔVGS. When the gate drivercharges/discharges the gate charge of FET via the gate resistance RG,the capacitance that can be seen from the driver side is not CGD but Cm.When the inductance L of the motor becomes large, the capacitance Cm hasa large value rather than CGD and thus the gate-source voltage VGS isseldom changed even though the gate driver charges/discharges the gateof T1 in the ON/OFF operation. However, the Miller effect is effectiveonly when the drain potential VDS of the main FET (T1) can be changedfreely between the ground potential level (GND) and the power supplyvoltage (VB). At this time, since T1 is in the pinch-off range,ID=Gm*VGS is satisfied where Gm is a transfer conductance of T1. It isappreciated from this Equation that ID is not changed and is kept almostconstant if VGS becomes almost constant.

Suppose that, when the transistor T32 is turned ON and OFF in FIG. 5,the voltage at the minus input terminal of the comparator CMP3 is givenby VL and VH FIG. 7 respectively. In this circuit example, VL=3.03V andVH=8.82V are given. When the operating point of T1 moves rightward on ahorizontal line passing through the B point in FIG. 7 and the drainvoltage VDS exceeds the voltage VH, the output of CMP3 goes to the Hlevel and T1 is turned ON. In the actual circuit, because of a delay inthe circuit, T1 is turned ON after a while after the drain voltage VDSexceeds VH. In FIG. 7, T1 is turned ON at a C point at which the VDSexceeds 10V, and VDS goes down toward the ground potential level. WhenVDS is lowered smaller than the voltage VL, the output of CMP3 goes tothe L level and T1 is turned OFF once again. In this manner, T1continues the ON/OFF operation as far as the output of CMP2 is at the Llevel.

Reduction of ID by the ON/OFF Operation

Next, the event that the drain current ID is reduced gradually duringwhen the ON/OFF operation is continued will be explained hereunder.Since the drain voltage VDS of T1 is restricted by the referencevoltages VL and VH when the ON/OFF operation is started, the operatingpoint of T1 oscillates between the C point and the D point in FIG. 7.The average value of VDS at this time is at a G point and is locatedsubstantially in the center between the C point and the D point. The Gpoint is the DC-like operation point of T1. In contrast, a line segmentCD gives an AC operating curve. In FIG. 7, a straight line a gives aload line of T1 when the motor is stopped in the case where the powersupply device VB is set to 12.5V, and a gradient is decided by thearmature resistance Ra. Straight lines b to g are in parallel with thestraight line a, and their projections onto the axis of abscissa canrepresent an amount of the voltage drop respectively when the draincurrent ID (=the motor current) is supplied to the motor.

First, the situation immediately before the jamming occurs will beconsidered herein. The operation point of T1 at this time exists in theA point. Assume that the counter electromotive force of the motor isEmotor-A and the drain-source voltage is VDSon, Eq.(7) is given asfollows.VB=VDSon+Ra*ID+Emotor-A  Eq. (7)

Next, the situation immediately after the jamming occurs and then theON/OFF operation is started will be considered herein. ID consists of anAC component IDA that varies in synchronism with the ON/OFF operation,and a DC-like component IDD other than this IDA. That is, ID has arelationship ID=IDA+IDD. A counter electromotive force Eonoff isgenerated by the inductance of the motor when IDD is changed. Amagnitude of the force is calculated by Eq.(8).Eonoff=L*d(IDD)/dt  Eq.(8)

Assume that an average value of the drain-source voltage VDS of T1 inthe ON/OFF operation is VDSonoff. This corresponds to the G point inFIG. 7. Suppose that the number of revolution of the motor is notchanged in one period of the ON/OFF operation. In addition, since ID isnot changed, Eq.(9) is given.VB=VDSonoff+Ra*ID+Emotor−A+Eonoff  Eq.(9)

Subtracting both sides in Eq.(9) from both sides in Eq.(7) respectivelygives Eq.(10).0=VDSon−VDSonoff−EonoffEonoff=VDSon−VDSonoff  Eq.(10)where VDSon is a drain-source voltage in the continuous ON operation andis about 0.3 V, and VDSonoff is the voltage at the G point and is about6.5 V. Thus, Eonoff has a minus value of −6.2V from Eq.(10). Then, it isseen that IDD is reduced smaller than that in Eq.(8) because Eonoff hasthe minus value.

Implementation of the Minimum Reversing Load (Prevention of theMalfunction Caused Due to the Rough Road, or the Like)

When the DC-like component of the ID goes down from the operating pointG to the operating point H while executing the ON/OFF operation, theIref-f is reduced to follow IDD. Then, when IDD reaches the H point inFIG. 7, the CMP2 is inverted from the L level to the H level, theoperating point of FET T1 moves from the H point to the F point, and T1enters into its continuous ON state. When T1 is brought into itscontinuous ON state, ID is increased, the operating point goes to the Bpoint via the A point, and T1 enters into its ON/OFF operation onceagain. Since Iref-s is not changed for this while, the voltage at theplus input terminal of CMP2 is not changed and thus the A point is fixedand the B to F points are not changed correspondingly. The value of thecurrent ID is restricted within a predetermined range during when theON/OFF operation and the continuous ON state are repeated.

The average value of the current ID that is restricted within thepredetermined range is maintained at the value that is slightly largerthan the value of the current ID immediately before the current limitingoperation is executed. This condition has two important meanings.

First, a motor torque can be limited within a predetermined range sincethe motor torque is in proportion to the current. Thus, the jamming loadcan be limited.

Second, the malfunction such that the motor is reversed although thejamming does not occur during the running on the rough road, or the likecan be prevented. When the power window is operated during the runningon the rough road, or the like, it is possible that the driving force ofthe window glass is changed by the vertical motion of the car body andsuch driving force is increased momentarily, the number of revolution ofthe motor is lowered correspondingly, ID is increased, T1 is turned OFF,and the current limiting mode is applied. However, since the precedingglass driving force is still maintained even though the current limitingmode is applied, the number of revolution of the motor can be restoredinto the original state when the increase of the load due to thevertical motion is eliminated, so that the false reversion can beavoided. In this case, the premise that the glass driving force is notchanged for this while is needed. Also, this premise can be satisfied inmost cases. According to above features, the minimum reversing load canbe implemented under the condition that the false reversion is notcaused by the momentary increase of the driving force caused due to therough road, or the like.

Changes in the ON/OFF Operation Period and the Continuous ON PeriodAccording to the Reduction in the Number of Revolution of the Notor

Next, the case where Eq.(7) and Eq.(9) are generalized will beconsidered herein. The number of revolution of the motor is lowered whena time lapsed for a while after the jamming occurs. Since the counterelectromotive force of the motor is proportional to the number ofrevolution of the motor, a relationship of Emotor-B<Emotor-A is given ifthe counter electromotive force of the motor at that time is assumed asEmotor-B shown in FIG. 7. If T1 is brought into the continuous ON stateby the counter electromotive force having this lowered number ofrevolution, i.e., an magnitude of Emotor-B, the increasing rate of thecurrent ID is accelerated unlike the previous state, and thus a counterelectromotive force Eon is generated by the inductance L of the motor.Thus, Eon=L*dID/dt is derived. Rewriting Eq.(7) by using Eon, which isnot given in Eq.(7), gives Eq.(11).VB=VDSon+Ra*ID+Emotor-B+Eon  Eq.(11)

Suppose that the number of revolution of the motor in Equation of theON/OFF operation corresponding to Eq.(11) is not changed in both thecontinuous ON operation and the ON/OFF operation, replacing the Emotor-Ain Eq.(9) with the Emotor-B gives Eq.(12).VB=VDSonoff+Ra*ID+Emotor-B+Eonoff  Eq.(12)

Eq.(13) is derived from Eq.(11) and Eq.(12).Eon-Eonoff=VDSonoff-VDSon=6.5V−0.3V=6.2V  Eq. (13)

Because a sign of Eon is plus and a sign of Eonoff is minus, Eq.(13)signifies that the counter electromotive force Eonoff in the continuousON operation and the counter electromotive force Eonoff in the ON/OFFoperation have an opposite sign respectively and a sum of their absolutevalues becomes constant and is equal to a difference between respectiveVDSs, i.e., VDSonoff−VDSon. A difference between VDSs is constantregardless of the number of revolution of the motor. Since Emotor-Bbecomes small as the number of revolution of the motor is lowered, anabsolute value of Eonoff becomes small and an absolute value of Eonbecomes large. That is, it is understood that, when the number ofrevolution of the motor is lowered, the decreasing rate of ID in theON/OFF operation is lowered and the increasing rate of ID in thecontinuous ON operation is accelerated.

In addition, as can be seen from FIG. 7, Eonoff obtained when theoperation goes out of the ON/OFF operation (H point) (Eonoff-C in FIG.7) becomes small rather than Eonoff obtained immediately after theoperation enters into the ON/OFF operation (G point) (Eonoff-D in FIG.7). This indicates that a decreasing rate of the current is reducedgradually during the ON/OFF operation period. Also, the state that Eon-Eis smaller than Eon-F in FIG. 7 indicates that an increasing rate of thecurrent is reduced gradually during the continuous ON operation period.

Period of the ON/OFF Operation

When T1 is turned ON, the gate charge of T1 is discharged via R32 andthe gate-source voltage of T1 starts to reduce. Then, ID starts toreduce because ID=Gm*VGS. The counter electromotive force Ec isgenerated by the inductance L of the motor owing to the reduction of ID,and the voltage drop due to the armature resistance Ra is reduced thoughit is small. That is, the voltage drop of the motor is reduced by anamount of drop ΔVM (=Ec+Ra*ΔID). Where ΔID denotes an amount ofreduction of ID. Also, the counter electromotive force Ec can becalculated by Ec=L*ΔID/Δt. In this case, it is assumed that the numberof revolution of the motor is not changed during one period of theON/OFF operation.

The drain voltage VDS of T1 (which is equal to the drain-source voltagebecause the source is grounded) starts to increase because of an amountof drop ΔVM of the voltage drop of the motor. The gate-drain voltage ofT1 is extended by ΔVM and the gate-drain capacitance CGD is charged byΔVM. Since the charge is supplied to the gate by this charging, the gatecharge is not reduced even though the charge is discharged via R32.Therefore, the gate-source voltage VGS is substantially scarcelyreduced. This is the Miller effect.

Then, VDS is increased if the discharging still continues via R32, andthen T1 is turned OFF when VDS exceeds the reference voltage VH. Then,the current flows into the gate of T1 from the power supply voltage VBvia the resistors R31 and R32 and thus the gate starts to be charged.When the gate-source voltage VGS starts to increase owing to thecharging of the gate, ID increases and the gate charge is absorbed bythe Miller effect, as in the case of the discharging of the gate charge.That is, the charges charged via R31 and R32 are canceled by the Millereffect. Then, VDS is lowered when the charging of the gate proceeds,then the output of CMP3 goes to the L level when VDS becomes smallerthan the reference voltage VL, and then T1 is brought into its OFFstate.

A quantity of charge being supplied/canceled to/from the gate of T1 bythe Miller effect is decided by the reference voltages VL and VH, andhas a constant amount. A time required by the gate circuit to charge andsubsequently discharge this quantity of charge gives one period of theON/OFF operation. A charging time of the gate is decided by the powersupply voltage VB and the gate resistances R31+R32, and a dischargingtime is decided by the gate resistance R32. That is, the period of theON/OFF operation is decided by the reference voltages VL and VH, thepower supply voltage VB, and the gate resistances R31 and R32.Therefore, the period of the ON/OFF operation can be varied by changingthe gate resistances, more particularly the resistance R32.

3. Explanation of the Jamming Determining Circuit 6

3-1. Circuit Configuration of the Jamming Determining Circuit 6

The jamming determining circuit 6 in FIG. 5 has an input terminal thatis connected to the output terminal of CMP3 in the current limitingcircuit 7, and can be composed of a 16 pulse counter that is reset if itdoes not count for 80 μsecond.

3-2. Explanation of the Operation of the Jamming Determining Circuit 6

The power-window jamming preventing apparatus senses the jamming by thecurrent sensing circuit 2, then limits the current by the currentlimiting circuit 7 to keep the motor current ID within the predeterminedrange, and then determines by the jamming determining circuit 6 whetheror not the jamming occurs. A determining method will be explainedherein. When the number of revolution of the motor is lowered by thejamming, the ON/OFF operation period of T1 is prolonged while thecontinuous ON operation period of T1 is shortened. It is determined byutilizing this characteristic whether or not the jamming occurs. Thereare three following methods as the particular determining method.

(a) The occurrence of the jamming is determined when a ratio of thecontinuous ON operation period and the ON/OFF operation period reaches apredetermined value while sensing the ratio. The continuous ON operationperiod and the ON/OFF operation period can be discriminated based on theoutput of CMP2. The operation is the continuous ON operation when theoutput of CMP2 is at the H level, and the operation is the ON/OFFoperation when the output of CMP2 is at the L level. Therefore, a targetratio can be sensed if the output of CMP2 is averaged as the analogsignal.

(b) The occurrence of the jamming is determined when the continuous ONoperation period or the ON/OFF operation period reaches a predeterminedvalue while counting the period. The determination is made by countingthe H period or the L period of the output of CMP2.

(c) The occurrence of the jamming is determined when an ON/OFF frequencyin the ON/OFF operation period reaches a predetermined value whilecounting the frequency. The leading frequency of the output level ofCMP3 is counted, as shown in FIG. 5, and then the occurrence of thejamming is determined when the counted frequency reaches 16 pulses inthe example in FIG. 5. In order not to count the frequency in thecontinuous ON operation period, the counter is reset when the pulse isinterrupted for a predetermined period. In the example in FIG. 5, thecounter is reset when the output of CMP3 is not changed for 80 μs. Thenumber of revolution when the occurrence of the jamming is determined isset to a state in which such number of revolution is lowered by about60% rather than the number of revolution prior to the occurrence of thejamming. This set value is at a level that is not generated by reductionin the number of revolution caused by the impulsive load change that isgenerated due to the rough road, or the like.

Method of Setting a Jamming Determining Value

A method of setting a jamming determining value is summed up as follows.

(i) A determining value is set at a level that is not generated byreduction in the number of revolution of the motor caused by theimpulsive load change that is generated due to the rough road, or thelike.

(ii) A continued period of the ON/OFF operation depends on the OFF delaytime of T1 and the response characteristic of the OP amplifier used asCMP1. Therefore, the ON/OFF frequency corresponding to the determiningvalue is decided based on standard values of these characteristics asthe premise, and then a counter value is set.

(iii) When the determining value must be adjusted because the OFF delaytime of T1 and the response characteristic of the OP amplifier arevaried, the ON/OFF operation period is changed by varying the gateseries resistance of T1 to deal with these variations. Accordingly, thecounter value can be fixed even though the OFF delay time of T1 and theresponse characteristic of the OP amplifier are varied. It is convenientfor the case where respective circuits are prepared as IC that thecounter value can be fixed.

Change in the Number of Revolution of the Motor in the ON/OFF Operation

Explanation is made of the situation that the ON/OFF operation period isextended but the continuous ON operation period is shortened when thenumber of revolution of the motor is lowered. This explanation is madebased on the assumption. That is, the assumption that the number ofrevolution of the motor is seldom changed in one period of the ON/OFFoperation is made. This assumption is realized by such a method that themotor continues to push the glass with a constant force during theON/OFF operation. Since the inter-terminal voltage of the motor is givenas VB-VDSonoff in the ON/OFF operation, a motor output Pm is given byEq.(14). $\begin{matrix}\begin{matrix}{{Pm} = {\left( \text{VB-VDSonoff} \right)*{ID}\text{-}{Ra}*{ID2}}} \\{= {\left( {\text{VB-VDSonoff-Ra}*{ID}} \right)*{ID}}} \\{= {\left( \text{Emotor-Eonoff} \right)*{ID}}}\end{matrix} & {{Eq}.\quad(14)}\end{matrix}$

Followings can be understood by Eq.(14).

(i) In the ON/OFF operation, the almost constant output is outputirrespective of the number of revolution of the motor.

(ii) In the ON/OFF operation, the output is lowered by VDSonoff*IDrather than the output in the continuous ON operation.

In other words, the motor outputs the constant output during the ON/OFFoperation to drive the window glass. This means the motor continues topush the window glass, and the number of revolution of the motor isalways linked with the speed of the window glass. Since the motion ofthe window glass is slow, such motion is seldom changed within oneperiod of the ON/OFF operation. As a result, the number of revolution ofthe motor is also seldom changed within one period of the ON/OFFoperation, so that the above assumption can be supported.

FIG. 9 is a circuit diagram showing a modified example of the powerwindow jamming preventing apparatus of FIG. 5. The power window jammingpreventing apparatus shown in FIG. 90 differs from the power windowjamming preventing apparatus of FIG. 5 in current following circuits 3and 13. According to the current following circuit 13, the secondcharging and discharging circuit R22, C2 and the resistor R28 forcoupling the ungrounded sides of C1 and C2 are removed from the currentfollowing circuit 3 and the resistance value of the resistor R21 ischanged in order to maintain the time constant of the first chargingcircuit in accordance with the change.

The change brings about a case in which the time constant of the secondcharging and discharging circuit of FIG. 5 is nullified and the followupspeed of the component Iref-f having the fast followup speed of thereference current Iref is made to be infinitive. Therefore, althoughoperation of the power window jamming preventing apparatus of FIG. 9 isbasically the same as that of the circuit of FIG. 5, particularly, theoperation of the circuit 13 can also be interpreted as follows.

The second charging and discharging circuit is eliminated, the currentIref-f flowing in the second source follower circuit becomes 1 n-th ofthe motor current ID always including that in the On/Off operation timeand the voltage generated across both ends of the resistor R24 becomesas shown by Eq. (15) in comparison with the voltage generated across theboth ends of the shunt resistor R1. $\begin{matrix}\begin{matrix}{{{Iref}*{{R24}/\left( {{ID}*{R1}} \right)}} = {{R24}/\left( {n*{R1}} \right)}} \\{= {1.5\quad k\quad{\Omega/\left( {1618*0.034\quad\Omega} \right)}}} \\{= {27.3.}}\end{matrix} & {{Eq}.\quad(15)}\end{matrix}$

That is, a voltage constituted by amplifying the voltage drop of theshunt resistor R1 in proportion to the motor current ID in proportion tothe motor current ID by 27.3 times is generated across both ends of theresistor R24 and a voltage averaging the voltage by an integratingcircuit comprising R21 and C1 is generated across the both ends of theresistor R23. The respective generated voltages are operated to compareby CMP2.

FIG. 10 is a circuit diagram showing a modified example of the powerwindow jamming preventing apparatus of FIG. 9. The power window jammingpreventing apparatus shown in FIG. 10 differs from the power windowjamming preventing apparatus of FIG. 9 in current following circuits 13and 14. Points of difference between the circuits and the following twopoints.

(a) A point that the drain terminal of the transistor T21 is connectednot to the reference resistor R20 but directly to the power source VB.

(b) A point that there are added a resistor R26 connected to the plusinput terminal of CMP1, and a transistor T23 a drain terminal of whichis connected to the resistor R26 a source terminal of which is groundedand a gate terminal of which is connected to the output terminal ofCMP2.

Explanation of Operation

The motor current ID is inverted to the voltage by the shunt resistorR1. CMP1 controls such that the plus input terminal voltage and theminus input terminal voltage are always equal to each other andtherefore, the current Iref flowing in the reference resistor R20 isproportional to ID such that Iref*n=ID. Therefore, when an amount ofchanging Iref when the motor current ID is changed by ΔID is designatedby notation ΔIref, ΔrIref*n=ΔID is established.

When jamming is not brought about, the transistor T23 is made On andtherefore, a current component Iref-2 of Iref is made to flow via R26and T23. That is, Iref=Iref-f+Iref-2 is established. Since Iref-2 cannotbe changed, all of the change of ΔIref of Iref is reflected to Iref-fand a voltage change ΔVR24 represented by Ep. (16) is generated in theresistor R24 in which Iref-f flows.ΔVR 24=ΔIref*R 24=(ΔID/n)*R 24  Eq. (16)

By taking a ratio of ΔVR24 to a voltage change ΔVR1 generated at theshunt resistor R1 (=ΔID*R1), as shown by Eq. (17), it is known that thevoltage change across the both ends of the shunt resistor R1 isgenerated across the both ends of the resistor R24 by being amplified by27.3 times. $\begin{matrix}\begin{matrix}{{\Delta\quad{{VR24}/\Delta}\quad{VR1}} = {\left( {{R24}/{R1}} \right)/n}} \\{= {\left( {1.5\quad k\quad{\Omega/34}\quad m\quad\Omega} \right)/1618}} \\{= 27.3}\end{matrix} & {{Eq}.\quad(17)}\end{matrix}$

Meanwhile, although there is a voltage difference constituted by summingup a forward direction voltage drop of the diode D21 and the voltagebetween the gate and the source of T22 between the output voltage ofCMP1 and the ungrounded side potential of R24, since the voltagedifference can be regarded as a constant value, a change in the outputof CMP1 is equal to a change in the ungrounded side potential of R24.Therefore, an amount of changing the ungrounded side potential of thecapacitor C1 is an amount ΔVR24 of changing the ungrounded sidepotential of R24 averaged by the time constant R21*C21. The ungroundedside potential of the capacitor C1 is reflected to the source terminalof the transistor T21, that is, the plus input terminal of CMP2 except adifference of a direct current voltage. Meanwhile, the ungrounded sidepotential of R24 is inputted to the minus input terminal of CMP1.However, a direct current potential difference of an amount of 0.7V ofthe forward direction voltage drop of the diode D21 is applied betweenthe plus input terminal and the minus input terminal.

Summarizing the above-described, the amount of change ΔID of ID isconverted into the voltage of ΔVR1 by the shunt resistor R1. ΔVR1constitutes ΔVR24 by being amplified by 27.3 times and applied to theminus input terminal of CMP2. A rate of converting current→voltage(ΔVR24/ΔID) at this occasion is represented by Eq. (18). $\begin{matrix}\begin{matrix}{{\Delta\quad{{VR24}/\Delta}\quad{ID}} = {27.3*{R1}*\Delta\quad{{ID}/\Delta}\quad{ID}}} \\{{= {27.3*34\quad m\quad\Omega}}\quad} \\{= {928\quad{mV}\text{/}A}}\end{matrix} & {{Eq}.\quad(18)}\end{matrix}$

Meanwhile, the plus input terminal of CMP2 is applied with an averagevalue of ΔVR24 and a direct current voltage difference of 0.7V isapplied between the plus input terminal and the minus input terminal.

The motor current ID includes the pulsating current component. When atotal amplitude of the pulsating current is set to 0.5 A, ΔVR24 includesan amount of varying the voltage of 928 mV*0.5 A=464 mV. That is, thereis a variation having a half amplitude of ±232 mV and therefore, when anincrease in voltage of 0.7V−0.232V=0.468V is generated, the output ofCMP2 is inverted from H level to L level. That is, 0.468V becomes ajamming detecting value. When 0.468V is converted into ID, the currentbecomes 0.5 A (=0.468V/R24*n). When ID is increased by 0.5 A, the outputof CMP2 is inverted.

When the output of CP2 becomes L level, the transistor T23 is made Offand the current Iref-2 which has been flowed in R26 and T23 isextinguished. At this occasion, since ID is not changed, the referencecurrent Iref remains unchanged. Therefore, Iref-f is increased by anextinguished amount of Iref-2. Thereby, the voltage drop of R24 isincreased and the minus input terminal voltage of CMP2 is increased. Anamount of the increase becomes Iref-2*R24. When the output of CMP2becomes at L level, the On/Off operation is started and ID is reduced.When an amount of reducing Iref by reducing ID exceeds Iref-2, CMP2 isinverted again to H level and ID is brought into the continuous On stateto start increasing. When the output of CMP2 becomes at H level, T23 ismade On, Iref-2 is made to flow, Iref-f is reduced by that amount andthe minus terminal voltage of CMP2 is lowered by Iref-2*R24. When anamount of increasing Iref by increasing ID exceeds Iref-2, CMP2 isinverted to L level. When the output of CMP2 becomes at L level, sincethere is a delay of making FET T1 Off, ID is increased during a timeperiod of the delay. Therefore, during the time period of L, the outputof CMP2 is obliged to reduce by including not only Iref-2 but also anamount of increasing ID by the delay.

A maximum value of the motor current ID during the current restrictingtime period of repeating the On/Off operation and the continuous Onoperation is an average value of ID before jamming added with thejamming detecting value of 0.5 A (0.468V) and a minimum current value isdetermined by a magnitude of Iref-2. Therefore, the average value of IDin the current restricting operation can arbitrarily be set by adjustingthe value of Iref-2.

The above-described is operation of the circuit of FIG. 10 and adifference thereof from the circuit of FIG. 5 is summarized below.

(i) Iref-f of FIG. 5 is not the change per se of ID. ΔIref-f*n≠ΔID isestablished. The potential difference generated across the both ends ofthe resistor R22 shows that there is a deviation between ID and Iref.Therefore, the voltage drop ΔVR24 generated at the resistor R24 byΔIref-f does not accurately represent ΔID. The value may be larger thanΔID or smaller than ΔID. That is, an amplitude of ΔVR24 is larger thanan amount in correspondence with ΔID. Therefore, the jamming determinantis substantially reduced to facilitate to start the On/Off operation.This signifies that there is increased a chance of erroneous operationby a variation in an impact load by a rough road or the like.

Meanwhile, in FIG. 10, ΔVR24 accurately represents ΔID and an influenceby a deviation from ΔID is not brought about.

(ii) According to the circuit of FIG. 5, in the On/Off operation time,the variation of the output of CMP1 is increased and saturated at Hlevel and L level. A deviation of the minus input terminal voltage ofCMP2 from ΔID is increased to differ from the change in ID. The plusinput terminal voltage of CMP2 remains unchanged and even when the minusinput terminal voltage is controlled by being compared with the plusinput terminal voltage, since ΔID does not coincide with the change inthe minus input terminal voltage of CMP2, when the motor revolutionnumber is reduced, ID is increased.

In contrast thereto, in FIG. 10, the change in the motor current isreflected to the minus terminal voltage of CMP2, a peak value incontrolling the current is maintained constant.

(iii) In FIG. 5, the time period of continuing the On/Off operation isdetermined by the delay in making T1 Off, the response delay of CMP1 andthe motor revolution number. Among them, the influence of the responsedelay time period of CMP1 is significant. Although a control of usingIref-2 can be carried out as in FIG. 10, even when Iref-2=0 A, there isa sufficient On/Off operation time period and when Iref-2 is used, theOn/Off operation time period is excessively prolonged, which is notpreferable in view of control. That is, the On/Off operation time periodcannot be controlled from outside. (However, in the system of FIG. 9making the followup speed of Iref-f infinitive, the control of usingIref-2 can be carried out). Meanwhile, in FIG. 10, although the delay ofT1 and the motor revolution number constitute factors of determining theOn/Off operation time period similar to FIG. 5, the response delay ofCMP1 does not effect influence thereon. Further, by using Iref-2, theOn/Off operation time period can substantially be controlled to anarbitrary value. When Iref-2 is increased, the On/Off operation timeperiod is prolonged and therefore, the minimum value of ID can bereduced. The maximum value of ID can be maintained constant and theminimum value can be controlled and therefore, the average current valueof ID in restricting the current can be set to a desired value.

(iv) In FIG. 5 and FIG. 9, Iref-s constituting a portion of Iref is madeto flow in cooperation with C1. When jamming is brought about and ID isincreased, the potential of C1 is hardly increased, however, thepotential is not nullified. Iref-s is increased in correspondence withan amount of increasing the potential of C1 and an amount of increasingIref-f is reduced by that amount. That is, the detection sensitivitybecomes dull by that amount. Meanwhile, in FIG. 10, although thepotential of C1 is increased similarly when jamming is brought about,the increase in C1 is not related to Iref and therefore, the increase inIref-f is not restrained by increasing C1. Therefore, a deterioration inthe detection sensitivity by increasing the potential of C1 is notbrought about and a further accurate control can be realized.

As is known from the above-described fact, the circuit of FIG. 10 ismore excellent than the system of FIG. 5 as the control of preventingjamming.

FIG. 11 shows a circuit diagram showing a modified example of the powerwindow jamming preventing apparatus of FIG. 5. The power window jammingpreventing apparatus shown in FIG. 1 differs from the power windowjamming preventing apparatus of FIG. 5 in the current sensing circuit 2.The current limiting circuit 7, the regularly rotating the reverselyrotating circuit 5 and the jamming determining circuit 6 stays the samealthough the circuits are simplified or omitted. Points of difference ofthe current sensing circuit 2 are the following two points.

(a) A point that the current following circuits 3 and 16 differ fromeach other. The current following circuit 16 is constituted by adding aresistor R29 connected to the plus input terminal of CMP1, a transistorT24 a drain terminal of which is connected to the resistor R29, a sourceterminal of which is grounded and a gate terminal of which is connectedto an output terminal of a starting timer 15, and a diode D22 an anodeterminal of which is connected to the capacitor C1 and a cathodeterminal of which is connected to the capacitor C2 to the currentfollowing circuit 3.

(b) A point of adding a starting timer 15 an input terminal of which isconnected to an input terminal of window up (Up) and the startingcircuit 4 connected to an output terminal of the starting timer 15 andthe current following circuit 16.

The starting circuit 4 includes:

nMOSFET (T42) a gate terminal of which is connected to the startingtimer 15 and a source terminal of which is grounded;

a resistor R43 connected to a drain terminal of T42;

pMOSFET (T41) a gate terminal of which is connected to the resistor R43and a drain terminal of which is connected to the plus terminal of thepower source VB;

a resistor R41 connected between the gate terminal and the drainterminal of T41; and

a resistor R42 connected to a source terminal of T41; and

a diode D41 an anode terminal of which is connected to the resistor R42and a cathode terminal of which is connected to the gate terminal ofT21;

Explanation of Operation

There is provided a rush current masking time period such that theOn/Off operation is not carried out by rise of the motor startingcurrent ID (rush current) when the motor is started by the window up(Up)or the window down (Down) signal. From a view point as a safetyapparatus, it is preferable to operate a jamming preventing functionimmediately after starting the motor. According to a system using apulse sensor, since a resolution of a pulse is poor and a time period isneeded for stabilizing the pulse and therefore, it is difficult tooperate the jamming preventing function immediately after starting themotor. Meanwhile, according to a current detecting system used in thecircuit, the response is fast and therefore, the jamming preventingfunction can be operated immediately after starting and a function as asafety apparatus more excellent than that of the pulse sensor system canbe realized. FIG. 11 shows a circuit for realizing jamming prevention(jamming protection) immediately after starting.

When the Motor is Rotated During a Starting Masking Time Period

When the up or the down signal is inputted, the starting timer isoperated, the transistor T24 in the current sensing circuit is made On,a reference current Iref-1 is made to flow by a starting timer operationtime period. A magnitude of Iref-1 is determined by the power sourcevoltage and the resistor R29. Further, meanwhile, the transistor T42 inthe current sensing circuit is made On and T41 is made On. Thereby, thecapacitors C1 and C2 are charged to be proximate to voltages determinedby R42 and R22. Iref-1 is set such that a value constituted bymultiplying a total of reference currents at this occasion by n timesbecomes larger than the motor rush current. That is, Iref-1 is set suchthat a relationship of Eq. (19) is established.ID rush current maximum value<n*(Iref-s+Iref-f+Iref-1)  Eq. (19)

Thereby, during a starting timer time period, the output level of CMP1is at L level and therefore, the current flows through a path of thepower source voltage VB→the transistor T41→the resistor R42→the diodeD41→the diode D22→the resistor R22→the output of CMP1 and potentials ofthe capacitors C1 and C2 are represented by Eq. (20) and Eq. (21).C 1 potential=(VB-2*0.7V−CMP 1 output)*R 22/(R 42+R 22)+0.7V+CMP 1output  Eq. (20)C 2 potential=(VB-2*0.7V−CMP 1 output)*R 22/(R 42+R 22)+CMP 1output  Eq. (21)

The voltage drop in the forward direction of the diode is set to 0.7V.According to the circuit example, the power source voltage VB=12.5V, theCMP output L level=2V, R42=3KΩ, R22=5.1KΩ and therefore, the potentialof C1=8.3V, the potential of C2=7.7V. When the starting timer isfinished, T43, T41 are made Off. At this occasion, when the motorcurrent is reduced and the output of CMP1 stays at L level, the electriccharge of C1 and C2 is discharged through a path of the diode D22→theresistor R22→the output of CMP1 to immediately enter followup operation.Therefore, when jamming is brought about under the state, the motor canbe stopped by immediately detecting jamming.

When the Motor is Not Rotated After Starting (Inputting the Window UpSignal)

In this case, at a time point of finishing the starting timer, a motorlock current is made to flow and therefore, the output of CMP1 becomes Hlevel and the potential of C2 is immediately charged up to the output ofH level of CMP1 via the resistor R22=5.1K. Meanwhile, the potential ofC1 is hardly raised since C1 is charged by a long time constant.Therefore, the minus input terminal voltage becomes higher than the plusinput terminal voltage of CMP2 and the output of CMP2 becomes L level.Even when T1 carries out the On/Off operation, the continuous On is notcarried out thereby and therefore, jamming determination is immediatelycarried out and reversely rotating operation is carried out.

Even when the motor is rotated after starting, in the case in which theoutput of CMP1 is at H level at a time of finishing the starting timer,the On/Off operation is immediately started. When the motor current IDis reduced during the time period of continuing the On/Off operation andthe continuous On operation, the motor is started to be operatednormally to continue rotating and when the motor current is increased byjamming, jamming is determined and the motor is operated rotatereversely, it is necessary to set R41, R22 such that the motor is notrotated reversely although jamming is not brought about.

Although according to the above-described power window jammingpreventing apparatus and other embodiment and modified examplesdisclosed in JP-A-2002-295129, the motor current can be restricted byswiftly determining jamming of a foreign matter without erroneousrecognition, it is further preferable to promote a function ofpreventing erroneous reverse rotation of the power-window motorparticularly when the voltage is low (that is, when the power sourcevoltage supplied from the power source supply apparatus is low).

SUMMARY OF THE INVENTION

The present invention has been made in light of the above circumstances,and it is an object of the present invention to provide an improvedpower-window jamming preventing apparatus capable of limiting a motorcurrent by sensing surely an abnormal current caused in a motor currentdue to a jamming of a foreign matter without error in the power-windowjamming preventing apparatus that can sense the jamming of the foreignmatter in a window glass based on change in the motor current.

In order to achieve the above object, according to the presentinvention, there is provided a power-window jamming preventingapparatus, comprising:

a current sensing circuit, which senses a motor current flowing througha motor for driving a window glass;

a current limiting circuit, which increases and decreases the motorcurrent based on a current-limitation control signal outputted from thecurrent sensing circuit when an amount of increase of the motor currentexceeds a predetermined vale; and

a jamming determining circuit, which determines a jamming of a foreignmatter in the window glass based on increase of the motor current toreverse a rotation of the motor,

wherein the current sensing circuit includes;

-   -   a shunt resistor, on which the motor current is flown;    -   a reference resistor, which has a resistance value that is n        times the shunt resistor; and    -   a current following circuit, which increases and decreases a        reference current that flows through the reference resistor and        is 1/n of the motor current, based on a voltage applied to the        shunt resistor;

wherein the current following circuit includes:

-   -   a reference current controlling circuit, which controls        increase/decrease of the reference current, and generates a        first reference voltage which is lowered according to increase        of the motor current, and a second reference voltage which is        higher than the first reference voltage, based on the reference        current;    -   a first comparator, which has a first input terminal to which        the first reference voltage is applied; and    -   a charging/discharging circuit, which generates a third        reference voltage in compliance with a charge/discharge        controlling signal outputted from the first comparator and        outputs the third reference voltage to a second input terminal        of the first comparator, the third reference voltage indicating        an average value of the first reference voltage, and the        charge/discharge controlling signal being shifted alternately to        two voltage levels, and

the apparatus, further comprising a potential difference generatingcircuit, which monitors a power source voltage supplied to the currentsensing circuit and the power window motor, and which clamps the thirdreference voltage so as to drop a constant voltage from the thirdreference when the power source is low such that a potential differencebetween the second reference voltage and the third reference voltage iskept greater than a predetermined voltage.

According to the above configuration, the potential differencegenerating circuit of the power window jamming preventing apparatusmonitors the power source voltage supplied to the current sensingcircuit and the power window motor and clamps the third referencevoltage when the power source voltage is low to always subject to theconstant voltage drop, thereby, the potential difference between thesecond difference voltage and the third difference voltage is preventedfrom being equal to or lower than the predetermined voltage andtherefore, in comparison with the power window jamming preventingapparatus of the prior art, there is promoted the function of preventingthe power window motor from being erroneously rotated reversely when thepower source voltage is a low voltage. Further, a value of the voltagedrop of the third reference voltage by the potential differencegenerating circuit is to be set such that the second reference voltageis equal to or lower than the third reference voltage when jamming isbrought about and by setting in this way, even immediately afterstarting the power window motor, when jamming is brought about and theamount of increasing the motor current exceeds the predetermined value,the power window motor can swiftly and firmly be rotated reversely byswiftly and firmly reducing the motor current by the current restrictingcircuit and determining jamming without erroneous recognition from theincrease in the motor current by the jamming determining circuit.

Preferably, the potential difference generating circuit includes: apower source voltage monitoring circuit, which monitors the power sourcevoltage to determine whether or not the power source voltage is low, andwhich outputs a clamp circuit control signal based on a result of adetermination of the power source voltage monitoring circuit; and aclamping circuit, which is provided in the charge/discharge circuit forclamping the third reference voltage so as to drop the constant voltagefrom the third reference in accordance with the clamping circuit controlsignal indicating that the power source voltage is low.

In the above configuration, there is promoted the function of preventingthe power window motor from being erroneously rotated reversely when thepower source voltage is the low voltage.

As described above, concise explanation has been given of the invention.Further, details of the invention will further be clarified by readingthe best mode for carrying out the invention explained below inreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail preferred exemplary embodimentsthereof with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram schematically showing a power window jammingpreventing apparatus which is an embodiment according to the invention.

FIG. 2A is a characteristic diagram (timing chart) showing respectivechanges of a motor current, a second reference voltage, a thirdreference voltage and an output of a comparator CMP2 from occurrence ofjamming in operating a power window to detection of jamming by the powerwindow jamming preventing apparatus of FIG. 1 and FIG. 2B is acharacteristic diagram (timing chart) showing respective changes of themotor current, the second reference voltage and the third referencevoltage of the power-window motor when a Vins−Vc potential differencegenerating circuit is operated in the power window jamming preventingapparatus of FIG. 1 and when the Vins−Vc potential difference generatingcircuit is not operated:

FIG. 3 is a block diagram of a power window jamming preventing apparatusof a related art:

FIGS. 4A to 4C illustrate block diagrams for explaining modifiedexamples of the power window jamming preventing apparatus of the relatedart:

FIG. 5 is a circuit diagram of the power window jamming preventingapparatus of the related art:

FIGS. 6A to 6C illustrate diagrams for explaining Onoff operation of acurrent sensing circuit of the power window jamming preventing apparatusof the related art:

FIG. 7 is a static characteristic curve diagram added with a load linefor explaining operation of a semiconductor switching element of acurrent limiting circuit of the power window jamming preventingapparatus of the related art:

FIG. 8 is an equivalent circuit diagram for explaining operation of thesemiconductor switching element of the current limiting circuit of thepower window jamming preventing apparatus of the related art:

FIG. 9 is a circuit diagram showing a modified example of the powerwindow jamming preventing apparatus of FIG. 5:

FIG. 10 is a circuit diagram showing a modified example of the powerwindow jamming preventing apparatus of FIG. 9; and

FIG. 11 is a circuit diagram showing a modified example of the powerwindow jamming preventing apparatus of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed explanation will be given of a preferable embodimentaccording to the invention in reference to the attached drawings asfollows. FIG. 1 is a circuit diagram schematically showing a powerwindow jamming preventing apparatus which is an embodiment according tothe invention, FIG. 2A is a characteristic diagram (timing chart)showing respective changes of the motor current ID, the second referencevoltage Vins, the third reference voltage Vc, and the output (CPOUT_B)of the comparator CMP2 reaching detection of jamming by the power windowjamming preventing apparatus of FIG. 1 from occurrence of jamming inoperating the power window, and FIG. 2B is a characteristic diagram(timing chart) showing respective changes of the motor current ID, thesecond reference voltage Vins and the third reference voltage Vc afterstarting the power-window motor 5 when a Vins−Vc potential differencegenerating circuit 16 b is operated in the power window jammingpreventing apparatus of FIG. 1 and when the Vins−Vc potential differencegenerating circuit 16 b is not operated.

The power window jamming preventing apparatus of the invention show inFIG. 1 is provided with an example of a circuit modifying the powerwindow jamming preventing apparatus of FIG. 5 as shown by FIG. 4C andFIG. 11 as has already been explained and modifying the power windowjamming preventing apparatus by using a resistor in place of the diodeD21 of the current sensing circuit 2. Specifically, according to thepower window jamming preventing apparatus of the invention, the shuntresistor R1 and the reference resistor R20 of the current sensingcircuit are arranged on the low side (that is, ground side) of thepower-window motor 5 and the circuit constitution of the currentfollowing circuit of the current sensing circuit is changed inaccordance therewith.

As shown by FIG. 1, the power window jamming preventing apparatus of theinvention includes a current sensing circuit 2 a for detecting anincrease in the motor current ID flowing in the power-window motor 5having the regularly rotating and reversely rotating circuit, thecurrent limiting circuit 7 for reducing and increasing the motor currentID in a predetermined range in accordance with the current restrictingcontrol signal CPOUT_B outputted from the current sensing circuit 2 awhen the amount of increasing the motor current ID exceeds apredetermined value, and the jamming determining circuit 6 connected tothe current limiting circuit 7 and the power-window motor 5 fordetermining jamming from the increase in the motor current ID. Further,constitutions of the power-window motor 5, the jamming determiningcircuit 6 and the current limiting circuit 7 are substantially the sameas the circuit constitutions of the power window jamming preventingapparatus of FIG. 5.

The current sensing circuit 2 a includes the shunt resistor R1 which isconnected in series with the power-window motor 5 and the currentlimiting circuit 7, one end of which is connected to the minus terminal(that is, ground terminal; ground) of the power supply device VB and inwhich the motor current ID is made to flow from the power supply deviceVB, the reference resistor 20 which is provided with the resistancevalue of n times of that of the shunt resistor R1 and one end of whichis connected to the minus terminal of the power supply device VB, acurrent following circuit 16 a connected to respective other ends of thereference resistor R20 and the shunt resistor R1 for increasing andreducing the reference current Iref flowing to the reference resistorR20 based on the voltage applied to the shunt resistor R1, thecomparator (second comparator) CMP2 the plus input terminal and theminus input terminal of which are connected to the current followingcircuit 16 a and the output terminal of which is connected to MOR1(refer to FIG. 5) of the current limiting circuit 7, the resistor R25connected between the 5V power source and the output terminal of CMP2for pulling up the current-limitation control signal CPOUT_B, a startingcircuit 4 a connected to the current following circuit 16 a forproviding the rush current masking time period such that the On/Offoperation is not carried out by the rise current (that is, rush current)of the motor current ID in starting the power-window motor 5, a startingtimer 15 a connected to the starting circuit 14 a and connected to anoutput terminal of an OR circuit OR1 for calculating a logical sum ofH/L level of the window down signal (Down) and the window up signal (Up)for instructing to open and close the window glass. Further, thestarting timer 15 a may not be provided as a constituent element of thecurrent sensing circuit 2 a.

The current following circuit 16 a includes a reference current controlcircuit for controlling to increase or reduce a reference currentconstituting 1 n-th of the motor current ID. The reference currentcontrol circuit includes a resistor R24 one end of which is connected tothe wire 1, a resistor R27 one end of which is connected to other end ofthe resistor R24 and a line connecting to the resistor R24 of which isconnected with the plus input terminal of CMP2, pMOSFET T22 providedbetween the resistor R27 and the reference resistor R20 such that adrain terminal thereof is connected to other end of the resistor 27 anda source terminal of which is connected to other end of the referenceresistor R20, an operational amplifier AMP1 a plus input terminal ofwhich is connected to a source terminal of T22 and an output terminal ofwhich is connected to a gate terminal of T22, a resistor of R30 one endof which is connected to a minus input terminal of the operationalamplifier AMP1 and other end of which is connected to the other end ofthe resistor R1, a resistor R23 one end of which is connected to thewire 1, a PNP type bipolar transistor T23 an emitter terminal of whichis connected to other end of the resistor R23 and a collector terminalof which is connected to the source terminal of T22, and an operationalamplifier AMP2 a minus input terminal of which is connected to theemitter terminal of T23, an output terminal of which is connected to abase terminal of T23 and a plus input terminal of which is connected toa minus input terminal of CMP2.

The operational amplifier AMP1 applies a pertinent voltage from theoutput terminal to the gate terminal of T22 to control such that thecurrent Iref-f is made to flow from T22 to the reference resistor R20 inaccordance with an increase or a reduction in the motor current IDflowing to the shunt resistor R1. According to the control, when themotor current ID is increased, an input terminal voltage of AMP1 isinstantaneously increased and therefore, the voltage applied from AMP1to the gate terminal of T22 is increased to make the current Iref-f flowto increase and conversely when the motor current ID is reduced, theinput terminal voltage of AMP1 is instantaneously reduced and therefore,the voltage applied from AMP1 to the gate terminal of T22 is reduced tomake the current Iref-f flow to reduce. Further, although the resistorR30 is provided between the minus input terminal AMP1 and the shuntresistor R1, the resistor R30 is a resistor for adjusting an inputimpedance of AMP1 and may not be provided. When the resistor R30 is notprovided, the reference current Iref is made to flow to the referenceresistor R20 such that voltages respectively applied to the shuntresistor R1 and the reference resistor R20 are always equal to eachother.

The current following circuit 16 a is further provided with the firstcomparator CMP1 the minus input terminal of which is connected to theplus input terminal of the operational amplifier AMP2 and the plus inputterminal of which is connected to the drain terminal of T22 (that is,the other end of the resistor R27), and a charging and dischargingcircuit. The charging and discharging circuit includes a capacitor C1one end of which is connected to the wire 1 and other end of which isconnected to the minus input terminal of AMP1, a resistor R390 one endof which is connected to the wire 1, a PNP type bipolar transistor T65an emitter terminal of which is connected to the other end of theresistor R390, a Vins−Vc potential difference generating circuit 16 bconnected to a collector terminal of T65, an NPN type bipolar transistorT66 a collector terminal of which is connected to the Vins−Vc potentialdifference generating circuit 16 b and the minus input terminal of CMP1(otherwise, the other end of C1 and the like), a first semiconductorswitch SSW1 connected between a base terminal of T66 and the minusterminal of the power supply device VB and connected to the outputterminal of CMP1 for being operated to On/Off in accordance with theoutput of CMP1 (CMP1_OUT), a resistor R420 one end of which is connectedto an emitter terminal of T66 and other end of which is connected to theminus terminal of the power supply device VB, a resistor R281 one end ofwhich is connected to the wire 1, a PNP type bipolar transistor T67 anemitter terminal of which is connected to other end of the resistor R281and a base terminal of which is connected to a base terminal of T65, anNPN type bipolar transistor T68 a collector terminal and a base terminalof which are connected to a collector terminal of T67 and a baseterminal of T66, a resistor R282 one end of which is connected to anemitter terminal of T68 and other end of which is connected to the minusterminal of the power supply device VB, a resistor R121 one end of whichis connected to the wire 1, a PNP type bipolar transistor T69 an emitterterminal of which is connected to other end of the resistor R121 and abase terminal and a collector terminal of which are connected to a baseterminal T67, a third semiconductor switch SSW3 one end of which isconnected to the collector terminal of T69 for being operated On/Off inaccordance with charging and discharging permitting/prohibiting signalsoutputted from a control apparatus (not illustrated), a resistor R122one end of which is connected to other end of SSW3 and other end ofwhich is connected to the minus terminal of the power supply device VB.Further, in a normal state (that is, when the capacitor C1 is permittedto charge and discharge), the semiconductor switch SSW3 is brought intoan On state in accordance with the charging and dischargingpermitting/prohibiting signals to shortcircuit the circuit, thereby, thebase terminal voltage of T69 is reduced and a current is made to flowfrom the resistor R121 (wire 1) to the resistor R122 (the minus terminalof the power supply device VB).

The Vins−Vc potential difference generating circuit 16 b includes apower source voltage monitoring circuit 16 ba connected to the wire 1and the monitoring the power source voltage VB, and a clamping circuit16 bb connected between the collector terminal of T65 and the collectorterminal of T66. The power source voltage monitoring circuit 16 baincludes a resistor R520 one end of which is connected to the wire 1, aresistor 521 one end of which is connected to other end of the resistorR520 and other end of which is connected to the minus terminal of thepower supply device VB, a third comparator CMP4 a minus input terminalof which is connected to a connecting line of R520 and R521, and areference voltage source RV1 connected between a plus input terminal ofCMP4 and the minus terminal of the power supply device VB and applying areference voltage to the plus input terminal of CMP4. Further, the powersource voltage monitoring circuit 16 ba may not be provided as aconstituent element of the current following circuit 16 a. Meanwhile,the clamping circuit 16 bb includes a second semiconductor switch SSW2connected between the collector terminal of T65 and the collectorterminal of T66 and connected to an output terminal of CMP4 for beingoperated to On/Off in accordance with an output (CC) of CMP4, and aseries of three diodes D621, D622, D623 connected in parallel with SSW2.According to the series of three diodes D621, D622, D623, in furtherdetails, an anode terminal of D621 is connected to the collectorterminal of T65, an anode terminal of D622 is connected to a cathodeterminal of D621, an anode terminal of D623 is connected to a cathodeterminal of D622 and a cathode terminal of D623 is connected to thecollector terminal of T66. The diodes D621, D622, D623 connected inseries in this way are for producing a desired potential difference (apotential difference of 2.1V when a forward direction voltage drop ofone diode is, for example, 0.7V) between the collector terminal of T65and the collector terminal of T66 by forward direction voltage dropsthereof. In this way, according to the embodiment, three of voltage dropcircuits (that is, D621, D622 and D623) are provided, however, a numberof these is pertinently selected in accordance with the desiredpotential difference. Further, resistors or the like may naturally beused as voltage drop circuits in place of the diodes D621, D622, D623.

According to the current following circuit 16 a, the first referencevoltage Vc2 which is a potential of the drain terminal of T22 (that is,the other end of the resistor R27) is inputted to the plus inputterminal of the comparator CMP1. Further, the second reference voltageVins applied to the plus input terminal of CMP2 shows a voltage valuehigher than that of Vc2 by an amount of the resistor R27. Further, thethird reference voltage Vc controlled to constitute the average value ofVc2 is generated by charging and discharging the capacitor C1 andapplied to the minus input terminal of CMP1 and the minus input terminalof CMP2. Vc2, Vins and Vc are generated by passing the reference currentIref through a reference current control circuit and a differencebetween Vc and Vc2 is made to be proportional to a difference between Vcand Vins.

According to the operational amplifier AMP2, a current value of thecurrent Iref-s is constituted by dividing a voltage applied across bothends of the resistor R23 (that is, a difference voltage between apotential of the wire 1 and Vc) by a resistance value of R23 andtherefore, T23 is controlled such that the current Iref-s is made toflow to the resistor R23 by applying a pertinent voltage to the baseterminal of T23 from the output terminal. According to the control, whenthe motor current ID is increased, the input terminal voltage (Vc) isreduced by being delayed mainly by charging and discharging thecapacitor C1 and therefore, the voltage applied from AMP2 to the baseterminal of T23 is slowly reduced to make the current Iref-s flow toincrease and conversely, when the motor current ID is reduced, the inputterminal voltage (Vc) of AMP2 is increased by being delayed mainly bycharging and discharging the capacitor C1 and therefore, the voltageapplied from AMP2 from the base terminal of T23 is slowly increased toreduce the current Iref-s.

Further, the reference current Iref flowing in the reference resistorR20 is a total of the current Iref-f flowing through the resistor R24and the resistor R27 and the current Iref-s flowing through the resistorR23 and is a current in correspondence with one several thousandththrough several tens thousandth of the motor current ID similar to thecase of the circuit constitution of FIG. 11 and is pulsated similar tothe motor current ID. Notation Vins designates a potential between theresistor R24 and the resistor R27, and a potential the voltage of whichis dropped from Vins by a certain value by the resistor R27 andtherefore, Vc2 is also pulsated similar to Vins. However, pulsatingwaveforms of Vins and Vc2 are naturally reverse to a pulsating waveformof the motor current ID.

As described above, according to the charging and discharging circuit,when SSW 3 is brought into an ON state, operation of charging anddischarging the capacitor C1 is permitted. Specifically, first, when thecircuit is shortcircuited by SSW3, the base terminal voltage of T69 isreduced and T69 is brought into an ON state. Further, since the baseterminal voltage of T67 is the same as the base (collector) terminalvoltage of T69, T67 is brought into an On state, thereby, the baseterminal voltage of T68 is increased and T68 is brought into an On state(when SSW1 is brought into an Off state and the circuit is opened) andthe current is made to flow from the resistor R281 (wire 1) to R282 (theminus terminal of the power supply device VB). Meanwhile, since the baseterminal voltage of T65 is the same as the respective base terminalvoltages of T67 and T69, T65 is also brought into an On state, further,since the base terminal voltage of T66 is the same as the base(collector) terminal voltage of T68 (when SSW1 is brought into the Offstate and the circuit is opened), T66 is also brought into an On state.According to the power source voltage monitoring circuit 16 ba, avoltage having a value constituted by dividing the power source voltageVB (the voltage applied to the wire 1 by the power supply device VB) bythe resistor R520 and the resistor R521 is applied to the minus inputterminal of CMP4, the voltage is compared with the reference voltageapplied to the plus input terminal of CMP4 (outputted from the referencevoltage source RV1) at CMP4, when the voltage is equal to or higher thanthe reference voltage, the clamping circuit control signal (CC) at Hlevel is outputted from the output terminal of CMP4, SSW2 is broughtinto an On state and the circuit is shortcircuited, further, when thevoltage is equal to or lower than the reference voltage, the clampingcircuit control signal (CC) at L level is outputted from the outputterminal of CMP4, SSW2 is brought into an Off state and the circuit isopened.

When a pulsating voltage of Vc2 is equal to or higher than Vc, CMP1outputs the charging and discharging control signal (CMP1_OUT) at Hlevel and outputs the charging an discharging control signal (CMP1_OUT)at L level when VC2 is equal to or lower than Vc. In this way, CMP1outputs the charging and discharging control signal (CMP1_OUT)alternately changing the two voltage levels. When the semiconductorswitch SSW 1 receives CMP1-OUT at H level from CMP1, the circuit isshortcircuited and T66 is brought into the Off state, a current I ismade to flow from the wire 1 to the capacitor C1 via R390, T65 and theclamping circuit 16 bb to charge the capacitor C1. At this occasion,when SSW2 is brought into the On state, Vc becomes equal to the value ofthe collector terminal voltage of T65 (T66), and when SSW2 is broughtinto the Off state, Vc becomes equal to the value of the collectorterminal voltage of T66 the voltage of which is dropped from thecollector terminal voltage of T65 by the series of three diodes D621,D622, D623 (the case of the embodiment). Meanwhile, when thesemiconductor switch SSW1 receives CMP1_OUT at L level from CMP1, thecircuit is opened and T66 is brought into the On state, a current 2Itwice as much as the current I is made to flow from T66 and the resistorR420 to the ground (that is, the current I is made to flow from the wire1 via R390, T65 and the clamping circuit BB and the current I is made toflow also from the capacitor C1) and the capacitor C1 is discharged. INthis way, in the charging and discharging circuit, the stable referencevoltage Vc is generated by charging and discharging the capacitor C1 andis controlled to follow Vins.

According to the power window jamming preventing apparatus of FIG. 1, asshown by FIG. 2A, when jamming is brought about in operating to move upthe window glass and the motor current ID is rapidly increased, the plusinput terminal voltage (Vins) of CMP2 indicating an instantaneous valueof the motor current ID is lowered, and also the minus input terminalvoltage (Vc) is slowly lowered by retardedly following lowering of Vinsby charging and discharging the capacitor C1. Further, Vins and Vc crosseach other (that is, the potential of Vins becomes equal to or lowerthan the potential of Vc) and during the crossing time period, theoutput of CMP2 (CPOUT_B) is changed from H level to L level. Further,when CPOUT_B becomes L level, the semiconductor switching element T1(refer to FIG. 5) is controlled to On/Off in the current limitingcircuit 7, the number of times of On/Off during the On/Off operationtime period is counted by the jamming determining circuit 6 based on thenumber of times of rise of the output level of CMP3 (refer to FIG. 5) ofthe current limiting circuit 7 and when the counted number reaches aconstant value (for example, 16 pulses), jamming is determined.

According to the power window jamming preventing apparatus of FIG. 1, atlow voltage time (when the power source voltage VB is low), a peak valueof the pulsating voltage of Vins becomes high and therefore, an interval(that is, potential difference) between Vins and Vc becomes small. Thepotential difference characteristic of Vins and Vc is significantlyindicated particularly at low temperature since a peak value of thepulsating current of the motor current ID becomes high. Hence, the powerwindow jamming preventing apparatus of FIG. 1 is provided with theVins−Vc potential difference generating circuit 16 b for clamping Vc bythe voltage dropping circuit (diodes (the case of the embodiment),resistors or the like) to provide the potential difference between Vinsand Vc such that the potential difference between Vins and Vc does notbecome equal to or lower than a certain predetermined voltage in lowvoltage time. Here, an explanation will be given in reference to FIG. 2Bshowing respective changes of the motor current ID, the second referencevoltage Vins and the third reference voltage Vc after starting thepower-window motor 5 when the Vins−Vc potential difference generatingcircuit 16 b is operated at the low voltage time and when the Vins−Vcpotential difference generating circuit 16 b is not operated (that is,SSW2 is always brought into the On state).

As shown by FIG. 2B, first, in starting the power-window motor 5, a rushcurrent (motor current ID) is produced, however, the starting circuit 4a stabilizes Vc by carrying out a masking process of Vc in accordancewith the control signal from the starting timer 15 a such that aninfluence is not effected from the rapid change in the motor current ID.At this occasion, the voltage applied from AMP1 to the gate terminal ofT22 stays to be under the low state (that is, T22 continues to be Off bysetting a threshold of AMP1 in this way), Vins (as well as Vc2) aremaintained at constant values and therefore, Vc and Vins similarlymaintained at the constant values and do not cross each other. Further,when the masking time period of carrying out the masking process by thestarting circuit 4 a is finished, Vc is rapidly increased to beproximate to Vins and follows Vins when normal. However, when the powersource voltage VB is low, the peak value of the pulsating voltage ofVins becomes high and therefore, the pertinent potential differencebetween Vins and Vc is not provided and when the Vins−Vc potentialdifference generating circuit 16 b is not operated, as shown by a dottedline in FIG. 2B, although the jamming is not brought about, Vc crossesVins, as a result, the power-window motor 5 is erroneously rotatedreversely. Meanwhile, in a state that the Vins−Vc potential differencegenerating circuit 16 b is operated, when the power source voltage Vb islower than the predetermined voltage, the clamping circuit controlsignal (CC) for always subjecting Vc to the constant voltage drop by thediodes D621, D622, D623 (the case of the embodiment) by turning Off SSW2of the clamping circuit 16 bb is outputted from CMP4 of the power sourcevoltage monitoring circuit 16 ba, and therefore, as shown by a bold lineof FIG. 2B, Vc follows Vins by providing the pertinent potentialdifference. Further, the operation of clamping Vc by the clampingcircuit 16 bb is continued during a time period in which the powersource voltage monitoring circuit 16 ba determines the power sourcevoltage Vb as the low voltage. Further, when jamming is operated in theclamping operation, as shown by FIG. 2A, Vins and Vc cross each other todetect jamming. Therefore, the clamping of voltage of Vc by the clampingcircuit 16 bb, in other words, the forward direction voltage drop by thediodes D621, D622, D623 (the case of the embodiment) is to be set to avalue by which Vins and Vc can cross each other when jamming is broughtabout.

In this way, according to the power window jamming preventing apparatus,at low voltage time (that is, when the power source voltage suppliedfrom the power supply device Vb is low), the power source voltagemonitoring circuit 16 ba determines the low voltage to control such thatthe potential difference between Vc and Vins does not become equal to orlower than a certain predetermined voltage (in other words, such thatVins does not become equal to or lower than Vc although jamming is notbrought about) by clamping Vc by the clamping circuit 16 bb andtherefore, a function of preventing the power-window motor 5 from beingerroneously rotated reversely is promoted in comparison with the powerwindow jamming preventing apparatus of the prior art.

Further, the invention is not limited to the above-described embodimentbut can pertinently be modified or improved. Other wise, modes, number,portions of arranging respective constituent elements and the like andnumerical values, waveforms and the like in the above-describedembodiment are arbitrary and not limited so far as the invention can beachieved thereby.

1. A power-window jamming preventing apparatus, comprising; a currentsensing circuit, which senses a motor current flowing through a motorfor driving a window glass; a current limiting circuit, which increasesand decreases the motor current based on a current-limitation controlsignal outputted from the current sensing circuit when an amount ofincrease of the motor current exceeds a predetermined vale; and ajamming determining circuit, which determines a jamming of a foreignmatter in the window glass based on increase of the motor current toreverse a rotation of the motor, wherein the current sensing circuitincludes; a shunt resistor, on which the motor current is flown; areference resistor, which has a resistance value that is n times theshunt resistor; and a current following circuit, which increases anddecreases a reference current that flows through the reference resistorand is 1/n of the motor current, based on a voltage applied to the shuntresistor; wherein the current following circuit includes: a referencecurrent controlling circuit, which controls increase/decrease of thereference current, and generates a first reference voltage which islowered according to increase of the motor current, and a secondreference voltage which is higher than the first reference voltage,based on the reference current; a first comparator, which has a firstinput terminal to which the first reference voltage is applied; and acharging/discharging circuit, which generates a third reference voltagein compliance with a charge/discharge controlling signal outputted fromthe first comparator and outputs the third reference voltage to a secondinput terminal of the first comparator, the third reference voltageindicating an average value of the first reference voltage, and thecharge/discharge controlling signal being shifted alternately to twovoltage levels, and the apparatus, further comprising a potentialdifference generating circuit, which monitors a power source voltagesupplied to the current sensing circuit and the power window motor, andwhich clamps the third reference voltage so as to drop a constantvoltage from the third reference when the power source is low, such thata potential difference between the second reference voltage and thethird reference voltage is kept greater than a predetermined voltage. 2.The apparatus as set forth in claim 1, wherein the potential differencegenerating circuit includes: a power source voltage monitoring circuit,which monitors the power source voltage to determine whether or not thepower source voltage is low, and which outputs a clamp circuit controlsignal based on a result of a determination of the power source voltagemonitoring circuit; and a clamping circuit, which is provided in thecharge/discharge circuit for clamping the third reference voltage so asto drop the constant voltage from the third reference in accordance withthe clamping circuit control signal indicating that the power sourcevoltage is low.